1. Field of the Invention
The present invention relates to moisture curable compositions and a method of curing moisture curable compositions.
2. Description of Related Art
It is well known that moisture can be used as agent in various systems. In some instances, the water reacts with certain functional groups so as to form part of the linking group. In other instances, the water provides the accelerator, catalyst or vehicle by which curing is achieved. Of the known moisture curable compositions, moisture curable polyurethanes are used for a variety of purposes. For example, moisture curable polyurethanes have been used as adhesives. However, one component, moisture curable adhesive compositions cure fairly slowly due to dependence on relative humidity and the rate of diffusion of atmospheric moisture into the bondline. Further, fixturing may be required.
U.S. Pat. No. 4,511,626 describes one-component, moisture-curable polyurethane adhesive, sealant and coating compositions useful in bonding articles to substrates. The compositions contain (a) prepolymer(s) derived from 4,4'-diphenylmethane diisocyanate, or isocyanate functional derivative(s) of 4,4'-diphenylmethane diisocyanate, and polyol(s) containing hydroxyl groups, and (b) bis[2-(N,N-dialkylamino)alkyl]ethers. The compositions require several days for cure-through by atmospheric moisture.
In U.S. Pat. No. 3,705,132, a moisture curable polyurethane coating composition is disclosed. The excess isocyanate groups in the composition react with moisture in the atmosphere in order to effect curing.
Published PCT Application No. WO 90/06332 discloses compounds which crosslink under the action of humidity and which cure through moisture generating compounds that contain molecular water dispersed into the base material and are activated by heating.
Certain silicone compositions can also be cured in the presence of water. For example, in U.S. Pat. No. 4,810,748, a silicone sealant composition is described which bonds to dolomite containing concrete after exposure to moisture. The composition is obtained by adding a silicone fluid having greater than 2 mole percent epoxy functionality to a sealant containing a hydroxyl endblocked polydiorganosiloxane, acetamidosilane chain extender, and crosslinking agent selected from the group consisting of triacetamidosilane and aminoxysilicon compound. The moisture for curing the composition is obtained from the atmosphere.
U.S. Pat. No. 4,978,706 describes a further silicone composition that is stable in the absence of moisture, but cures to an elastomer upon exposure to moisture, while U.S. Pat. No. 4,870,130 describes polysiloxane compositions which harden in the presence of moisture by elimination of alcohols and that are improved by the presence of stabilizing silyl derivatives of N-methyl benzamide.
Certain polysulfide compositions may also be cured in the presence of moisture. For instance, U.S. Pat. No. 3,659,896 describes an automobile windshield mounting and sealing means that is provided by a preformed, adhesive, curable sealing strip comprising a thiol terminated synthetic polymer, particularly a liquid polysulfide polymer. The polymer cures in the presence of atmospheric moisture under ambient room temperature and weather conditions.
U.S. Pat. No. 3,912,696 discloses a stable unitary liquid polymer composition that is protected from moisture and is capable of being shipped and stored in a single container. The composition can be deposited without agitation or intermixing with other materials and can be completely cured by contact with surroundings containing essentially only moisture. The composition essentially comprises a liquid polyalkylene polysulfide polymer containing a dispersed dormant curing agent which is activated by the presence of moisture and is present in amounts sufficient to cure the polymer and an alkaline desiccating deliquescent accelerating agent which maintains the polymer in dry condition during shipment and storage and attracts moisture from its surroundings after deposition in place to hasten the curing of the polymer by the curing agent.
U.S. Pat. No. 3,714,132 describes a unitary polysulfide polymer composition protected from moisture and capable of being stored in a stable condition in a single container without undergoing curing while being capable of being cured on contact with moisture in the atmosphere.
Despite developments in the art, there still exists a need for a moisture curable composition which is stable over time, but which effectively cures upon activation.